The interception of contraband, such as explosives, narcotics, and biological warfare agents, is an important issue in the effort to ensure public safety. Numerous technologies have been proposed to detect contraband, with each technology presenting its own set of strengths and weaknesses. It is desirable to quantify the detection performance of each technology to judge its viability. Of particular interest is the time required to search a specified region while maintaining a specified minimum probability of correct detection (PCD) and a specified maximum probability of false alarm (PFA). In order to achieve a desired PCD for an acceptable PFA, it is often useful to increase the search time, thereby limiting the throughput time through the search region. Overcoming environmental factors, which adversely affect the PCD, or noise, which may increase the PFA, can lead to further increases in search time. For example, although x-ray CAT-scan equipment is commonly used to inspect for contraband, these instruments generally take about 10 seconds to perform a scan. In addition, because standard x-ray instrumentation relies on indirect information such as shape and density, it generally cannot directly identify contraband material. Particularly problematic are sheet explosives. The ambiguity inherent in indirect detection produces degraded performance through increased PFA, which increases throughput time, and a decreased PCD, which allows contraband to pass through the screening procedure, in comparison to direct detection methods which have reduced ambiguity. Another commonly used method of detection is vapor-based or particulate trace-chemical analysis. Although these instruments are significantly less expensive and smaller than x-ray based systems, their performance is degraded by a large PFA because of their sensitivity to trace quantities. These systems typically perform analyses in seconds and either require physical contact with the scanned item, or a specially designed vapor capture method that disrupts the normal flow of activities.